These are low cost but handy connectors - mainly keeping your stuff connected direct to your pack, but can be used for tying things off with paracord, nylon straps or whatever you need to MacGyver up (young folks can just Google that reference). Pair this with our Outdoor Knots Guide Book
and this little things will work wonders for you.
Take 3 or 4 on every trip; a small price to avoid watching your only water bottle pop out of your pack and head down a 1,000 foot cliff.
Do note that these are not the weight-bearing, climber-style caribiners - those are in another zip code price-wise and are usually overkill for backpackers; limit the use for these to lightweight things.
These are 70mm sized with a spring-loaded opening - about a 2" interior opening.